The present invention relates to a method for the preparation of a shaped article of cured silicone rubber. More particularly, the invention relates to a method for the preparation of a shaped article of a silicone rubber obtained of a so-called room temperature-vulcanizable (RTV) silicone rubber composition curable by the mechanism of the hydrosilation reaction between aliphatically unsaturated hydrocarbon groups in the organopolysiloxane and silicon-bonded hydrogen atoms catalyzed by a platinum catalyst.
Needless to say, silicone rubbers are materials having excellent properties in many respects including heat resistance, cold resistance, weathering resistance, electric properties and the like and used in a wide variety of industrial fields. Among them, there are known several classes of so-called room temperature-vulcanizable (RTV) silicone rubbers curable at room temperature by several different mechanisms for the crosslink formation including those curable by the condensation reaction in contact with the atmospheric moisture and those curable by the mechanism of the so-called hydrosilation reaction which is an addition reaction between aliphatically unsaturated hydrocarbon groups, e.g. vinyl, in the organopolysiloxane and the hydrogen atoms directly bonded to the silicon atoms. These RTV silicone rubbers are very useful in the building and construction works as a material for sealing or caulking applicable in the site of building or construction and as a electric insulating material in various kinds of electric and electronic instruments.
In contrast to the wide versatility of these RTV silicone rubber compositions, a problem in them is that the organopolysiloxane as the major constituent in these compositions is necessarily limited to those having a relatively low degree of polymerization in consideration of the requirements for the material such as good workability, long-term storability, high reactivity in curing, good miscibility between components and the like so that the shaped articles obtained by fully curing the RTV silicone rubber composition have only relatively low mechanical strengths in comparison with those of the silicone rubber articles curable only by heating. In addition, RTV silicone rubber compositions formulated with an organopolysiloxane of low molecular weight, as a matter of course, has a low consistency or is even flowable before curing so that once shaped forms of the compositions cannot retain the desired form. Even an improved RTV silicone rubber composition having a putty-like consistency cannot retain the once shaped form for a sufficiently long time before curing. In other words, sufficient form-retainability of the uncured silicone rubber composition and high mechanical strengths of the cured silicone rubber article can be obtained only with a silicone rubber composition having a millable consistency or a consistency suitable for roll-milling while no RTV silicone rubber composition having such a millable consistency is known.
Therefore, it may be a useful improvement if a means is provided for the preparation of a silicone rubber shaped article by curing at room temperature without the problems of the above mentioned poor retainability of the shaped form before curing and the relatively low mechanical strengths of the cured rubber articles.